CLDN18 and gastric cancer: CLDN18-ARHGAP fusions are also common in a subset of diffuse type GC, including GSRCC.51,488CLDN18 gene encodes Claudin18 protein, a key component of tight junction, which functions to lock adjacent cells together to form a barrier between the external and internal environment.489 There are two Claudin18 isoforms, Claudin18.1 and Claudin18.2, which differ in the first exon of the CLDN18 gene.490 Claudin18.2 is mainly expressed by differentiated cells rather than stem cells of the gastric mucosa.490 The expression of Claudin18.2 is maintained in a large fraction of GCs.